Study Of Transition Metal Carbides And Oxides Compound As Electrode Material

Owing to the rapid development of electronic devices,such as digital cameras,laptops,electric vehicles,hybrid electrical vehicles,mobile phones and so on,rechargeable Li-ion batteries?LIBs?,with high energy densities,light weight,long cycle life,and environmental friendliness,have been considered to be the most promising energy-storage system.Graphite is currently the most widely used anode in LIBs,but as a commercial anode material,it still suffers from a relatively small low theoretical capacity of 372 mA h g^-1,which greatly limits its wide application.Therefore,tremendous work has been focused on searching for alternative anode materials with high theoretical capacity high theoretical capacity anode materials for the replacement of the currently used graphite,such as transition metal oxides?TMOs?and transition metal oxides hybrid.In this paper,transition metal carbide and oxide composite materials are prepared by different methods.The morphology,structure and properties of the materials are analyzed by XRD,SEM,TEM,TG,electrochemical workstation and other characterization methods.The main contents of this paper are as follows:1.Hybrid aerogel by dispersing Mo₂C@C core-shell nanocrystals into three-dimensional?3D?graphene?Mo₂C@C-GA?has been successfully prepared through two-step method.Firstly,carbon-coated MoO₂ nanocrystals are uniformly anchored on 3D graphene aerogel?MoO₂@C-GA?via hydrothermal reaction.Then the MoO₂@C-GA precursor is transformed into Mo₂C@C-GA after the following carbonization process.Furthermore,the freeze-drying step plays an important role in the resulting pore size distribution of the porous networks.Moreover,graphene aerogels exhibit extremely low densities and superior electrical properties.When evaluated as anode material for lithium ion batteries,Mo₂C@C-GA delivers excellent rate capability and stable cycle performance when compared with C-GA and Mo₂C nanoparticles.Mo₂C@C-GA exhibits the initial discharge capacity of 1461.4 m A h g^-1 at the current density of0.1 A g^-1,and retains a reversible capacity of 1089.8 mA h g^-1.Even at high current density of 5 A g^-1,a high discharge capacity of 623.5 mA h g^-1 can be still achieved.The excellent performance of Mo₂C@C-GA could be attributed to the synergistic effect of Mo₂C@C nanocrystals and the 3D graphene conductive network.2.Mo₂C/C hollow nanofbers are synthesized via a simple electrospinning method with a coaxial nozzle.The formation of hollow structure is mainly due to the extraction of mineral oil from the inner shaft.The formation mechanism of Mo₂C/C hollow nanofbers is investigated in detail and it is discovered that the high temperature and hydrogen atmosphere may be the main driving forces which convert Mo-PAN nanofbers into Mo₂C/C hollow nanofbers.The carbon shell of the Mo₂C/C hollow nanofbers acts as both conductive bond to increase electrical conductivity and structural skeleton to maintain the integrity of Mo₂C during Li⁺insertion/extraction to achieve both high specifc capacity and good cyclic stability.As an anode for lithium-ion batteries,the Mo₂C/C hollow nanofber electrode exhibits high specific capacity and long cycle life even at a large current density.Their charge and discharge capacities are 846.8 and 864.8mA h g^-1 in the 70th cycle at 0.1 A g^-1,respectively.Even at a high current density of 1 A g^-1,a capacity of 674.4 mA h g^-1 can be obtained after 300cycles.3.In this work,a facile co-precipitation approach has been developed to fabricate the Ni-NiCo₂O₄@ZnCo₂O₄ yolk-shell nano-tetrahedron composites,which significantly improve the structural stability and conductivity of composite material.As anode material for lithium ion batteries,the Ni-NiCo₂O₄@ZnCo₂O₄ is proven to exhibit excellent cycling and rate performance for lithium ion batteries,such as the charge capacity of 1571.9 mA h g^-1 after 70 cycles at 0.1A g^-1,1097.5 mA h g^-1 after 600 cycles at 1.0 A g^-1.